Stagewise equipment

In stagewise equipment, the design and scale-up is simple and is often determined from bench data. The stage efficiency is usually high, and the capacity is determined by the settler design necessary to achieve coalescence of the dispersed phases. For differential contactors, such as columns, the flow capacity is determined by the droplet size and the type of internals (see... 

From the usual plate-type distillation and absorption columns, it was but natural to attempt to devise stagewise equipment for G/S processing, for better heat economy and better utilization of the contacting media. But instability of the downcomer for solids transfer between stages remained for many years an unsolved hydrodynamic problem, and even to this data, the stable operation of many solids downcomers still depends on mechanical devices. 

Equipment for continuous steady-state operations can be broadly classified into two major categories, according to whether it operates in stagewise or in continuous-contact fashion. Stagewise equipment is sometimes assembled in multiple units to produce multistage effects, whereas continuous-contact equipment may provide the equivalent of many stages in a single device. 

Liquid-hquid contacting equipment may be generally classified into two categories stagewise and continuous (oifferential) contact. 

Chapter 3 concerns the dynamic characteristics of stagewise types of equipment, based on the concept of the well-stirred tank. In this, the various types of stirred-tank chemical reactor operation are considered, together with allowance for heat effects, non-ideal flow, control and safety. Also included is the modelling of stagewise mass transfer applications, based on liquid-liquid extraction, gas absorption and distillation. 

Equipment chosen for pilot plant operations should closely approximate the commercially available equipment that will be used eventually. Thus, it would be of little use to operate a pilot plant using stagewise contactors if dilferential contactors were to be employed in the actual commercial operation. 

There followed a brief discussion of equipment for carrying out solvent extraction in industrial practice, both by stagewise and differential contact. Some of the first principles for the design of differential contactors were outlined and the part played by the efficiency of extraction in continuous equipment was discussed. Finally there was an outline of methods for the control of solvent loss which forms probably the most important environmental aspect of the application of solvent extraction. 

The transfer of mass from one phase to another is involved in the operations of distillation, absorption, extraction, humidification, adsorption, drying, and crystallization. The principal function of the equipment used for these operations is to permit efficient contact between the phases. Many special types of equipment have been developed that are particularly applicable for use with a given operation, but finite-stage contactors and continuous contactors are the types most commonly encountered. A major part of this chapter, therefore, is devoted to the design aspects and costs of stagewise plate contactors and continuous packed contactors. 

In 1968, an electrolytic reduction process was proposed by A. Schneider and A. L. Ayers (6) to circumvent the above disadvantages. A research program was carried out in the Allied Chemical Corporation s laboratories during the years 1968 to 1972 to develop the process and equipment. The work resulted in the development of the Electropulse Column ( 7) for the continuous (differential) electrolytic uranium-plutonium partition process, which was later scaled up, fabricated, and installed in the Allied-General Nuclear Services reprocessing plant at Barnwell, South Carolina. About the same time, a stagewise electrolytic uranium-plutonium partition process was tested on a mini mixer-settler unit in Germany. (8)... 

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